JP2023013805A - Signal transmission cable - Google Patents

Abstract

To provide a signal transmission cable whose transmission characteristics are not easy reduced when bent.SOLUTION: A signal transmission cable 1 comprising a conductor 2, an insulator 3 covering the circumference of the conductor 2, a shield layer 4 covering the circumference of the insulator 3, and a sheath 5 covering the circumference of the shield layer 4, wherein between the insulator 3 and the shield layer 4, a plating base layer 6 is provided so as to cover the circumference of the insulator 3, the shield layer 4 has a plating layer 41 formed so as to be in contact with an outer peripheral surface of the plating base layer 6 and so as to cover the plating base layer 6, and the surface roughness of the outer peripheral surface of the plating layer 41 is smaller than the surface roughness of an inner peripheral surface of the plating layer 41.SELECTED DRAWING: Figure 1

Description

The present invention relates to a signal transmission cable.

Signal transmission cables for transmitting high-frequency signals are used as internal wiring of electronic devices such as imaging devices used for automatic driving and the like, smartphones and tablet terminals, or wiring of machine tools such as industrial robots. For example, a coaxial cable is used as the signal transmission cable.

As a conventional coaxial cable, a tape member such as a copper tape having a copper foil on a resin layer is spirally wound around an insulator to form a shield layer (for example, Patent Document 1). reference).

Japanese Patent Application Laid-Open No. 2000-285747

However, with the above-described conventional coaxial cable, when the coaxial cable is bent, gaps may occur in the overlapping portions of the tape members, or wrinkles may occur in the tape members. In such a case, the insertion loss (S21) and the change in characteristic impedance between the bent portion and the other portion (the unbent straight portion) may increase, and the transmission characteristics may deteriorate.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a signal transmission cable whose transmission characteristics are less likely to deteriorate when bent.

In order to solve the above problems, the present invention includes a conductor, an insulator that surrounds the conductor, a shield layer that surrounds the insulator, and a sheath that surrounds the shield layer. The signal transmission cable further comprises a plating underlayer provided between the insulator and the shield layer so as to cover the periphery of the insulator, wherein the shield layer covers the outer circumference of the plating underlayer It has a plating layer formed so as to contact the surface and cover the plating underlayer, and the surface roughness of the outer peripheral surface of the plating layer is smaller than the surface roughness of the inner peripheral surface of the plating layer. , providing cables for signal transmission.

According to the present invention, it is possible to provide a signal transmission cable whose transmission characteristics are less likely to deteriorate when bent.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the signal transmission cable which concerns on one embodiment of this invention, (a) is sectional drawing which shows a cross section perpendicular|vertical to a cable longitudinal direction, (b) is the photograph which expanded the cross section. It is a figure explaining formation of a plating layer. It is a figure which shows a blast processing apparatus, (a) is a perspective view, (b) is the top view seen from conveyance direction near side. FIG. 4 is a graph showing the measurement results of the surface roughness of the outer peripheral surface of the plating underlayer after blasting. FIG. 4 is a graph showing measurement results of an insertion loss S21, in which (a) shows the measurement results when the signal transmission cable is straight without bending, and (b) shows the measurement results when the signal transmission cable is bent with a bending radius of 1 mm. (a) is a graph showing measurement results of changes in characteristic impedance due to bending, and (a) is a graph showing an insertion loss S21 with respect to a bending radius and the characteristic impedance of a bent portion.

[Embodiment]
BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the accompanying drawings.

1A and 1B are diagrams showing a signal transmission cable according to the present embodiment, FIG. 1A being a sectional view showing a section perpendicular to the longitudinal direction of the cable, and FIG.

As shown in FIG. 1(a), a signal transmission cable 1 includes a conductor 2 arranged at the center of the cable, an insulator 3 surrounding the conductor 2, a shield layer 4 surrounding the insulator 3, and a sheath 5 covering the periphery of the shield layer 4 . That is, the signal transmission cable 1 is a coaxial cable including a conductor 2 as an inner conductor and a shield layer 4 as an outer conductor.

The signal transmission cable 1 is used, for example, as a fixed part cable for connecting a robot and a control device in a factory or the like, and has a length of, for example, about 25 m to 100 m. Further, when the signal transmission cable 1 is wired in an electronic device, its length is, for example, about 5 mm to 200 mm. Note that "covering" also includes the case of arranging through another layer. For example, other layers may be arranged between the conductor 2 and the insulator 3 or between the shield layer 4 and the sheath 5 .

(Conductor 2)
In the signal transmission cable 1 according to the present embodiment, the conductor 2 is formed by twisting a plurality of strands 2a and compressing the conductor 2 so that the cross-sectional shape perpendicular to the longitudinal direction of the cable has a predetermined shape such as a circular shape. made of compressed stranded conductors. In the present embodiment, a stranded conductor obtained by concentrically twisting seven strands 2a is passed through a die having a diameter smaller than that of the stranded conductor and having a circular exit, thereby compressing the conductor as shown in FIG. A conductor 2 having a circular cross section was formed as shown in FIG. The strand 2a arranged in the center has a substantially hexagonal shape in cross section, and the six strands 2a arranged in the periphery have a substantially fan shape in cross section. Moreover, it is preferable that the adjacent strands 2a are in contact (surface contact) so that no gap is formed between the strands 2a. Furthermore, the outer surface of the compressed stranded conductor is preferably smooth in the cable circumferential direction and the cable longitudinal direction. In the signal transmission cable 1 according to the present embodiment shown in FIG. 1, an example in which the conductor 2 is composed of a compressed twisted wire conductor having a circular cross-sectional shape is shown, but the cross-sectional shape is not circular. The conductor 2 may be composed of a compressed stranded wire conductor that is compressed into (for example, a polygonal shape such as a square shape). Since the conductor 2 is a compressed stranded wire conductor having a circular cross-sectional shape, the signal transmission cable 1 can be easily bent in any direction.

Ordinary stranded conductors that have not been compressed are more flexible and easier to bend than solid conductors. becomes lower. By using a compressed stranded wire conductor as the conductor 2 as in the present embodiment, the wires 2a are brought into close contact with each other and the gaps between the wires 2a are eliminated. Therefore, the conductor 2 using a compressed stranded conductor can have a lower conductor resistance than a normal stranded conductor with the same outer diameter. As a result, by using a compressed twisted wire conductor as the conductor 2, the electrical conductivity is improved and good attenuation characteristics are obtained. Furthermore, the current (simply referred to as current) that transmits the high-frequency signal mainly passes through the outer peripheral portion of the conductor 2 due to the skin effect. When the conductor 2 is composed of a stranded conductor obtained by twisting a plurality of strands 2a, the curvature of the strand is smaller than that of a single conductor having the same outer diameter as the stranded conductor. The cross-sectional area will be smaller than a solid conductor with the same outer diameter as a stranded conductor. On the other hand, in the present embodiment, by using a compressed stranded conductor obtained by compressing a stranded conductor as the conductor 2, the wires 2a are in close contact with each other, and the outer circumference of the conductor 2 is concentrically shaped like a single wire conductor. becomes. As a result, the conductor 2 made of a compressed stranded conductor has a larger cross-sectional area of the portion through which the current passes, compared to a stranded conductor having the same outer diameter, so that better attenuation characteristics can be obtained.

In order to obtain good attenuation characteristics, it is desirable that the electrical conductivity of the compressed stranded conductor used as the conductor 2 is 99% IACS or higher. In the present embodiment, an annealed copper wire made of silver-plated pure copper is used as the wire 2a of the conductor 2 in order to achieve high electrical conductivity. In addition, you may use the annealed copper wire which is not silver-plated as the strand 2a. In addition, by compressing through the die, strain is imparted to the wire 2a and the electrical conductivity is lowered, but after that, by performing heat treatment (annealing), the strain is removed and the conductivity is 99% IACS or more. rate can be achieved.

(Insulator 3)
The insulator 3 should have a dielectric constant as low as possible in order to improve the transmission characteristics of high frequency signals (more specifically, for example, to make it difficult to attenuate high frequency signals in the band of 10 MHz to 50 GHz when transmitted). It is desirable to use In this embodiment, the insulator 3 is made of fluorine resin. As the fluorine resin used for the insulator 3, FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), or the like may be used. The thickness of the insulator 3 is preferably 0.2 mm or more and 2.0 mm or less.

(Sheath 5)
A plating base layer 6 , a shield layer 4 and a sheath 5 are sequentially provided around the insulator 3 . The details of the plating base layer 6 and the shield layer 4 will be described later.

The sheath 5 is made of an insulating resin composition such as fluororesin, PVC (polyvinyl chloride), urethane, or polyolefin. In this embodiment, the sheath 5 is made of PFA, which is a fluororesin. As the fluorine resin used for the sheath 5, FEP may be used.

The sheath 5 is formed by extrusion molding, but if solid molding is performed, the resin constituting the sheath 5 will enter between the metal wires of the outer shield layer 42, which will be described later, and the signal transmission cable 1 will be hard and difficult to bend. It may become Therefore, in this embodiment, the sheath 5 is formed by tube extrusion. This prevents the resin forming the sheath 5 from entering between the strands of the outer shield layer 42 , thereby separating the sheath 5 and the outer shield layer 42 . That is, in the present embodiment, the sheath 5 and the outer shield layer 42 are not adhered to each other, so that the outer shield layer 42 can move relatively freely within the sheath 5 . This makes the signal transmission cable 1 easier to bend.

(Plating base layer 6)
The signal transmission cable 1 according to the present embodiment includes a plating base layer 6 provided between the insulator 3 and the shield layer 4 so as to cover the periphery of the insulator 3 . The plating base layer 6 is a layer that serves as a base for forming the plating layer 41 to be described later, and is particularly a layer for making the inner surface of the plating layer 41 have a predetermined surface roughness Ra. In the present embodiment, fluororesin is used as the insulator 3, and it is difficult to directly form the plating layer 41 on the fluororesin. A plating base layer 6 serving as a base is provided.

The plating base layer 6 is preferably made of an insulating resin capable of forming a plating layer 41 on its outer peripheral surface. Although the plating base layer 6 made of PE (polyethylene) is used in this embodiment, the plating base layer 6 made of PP (polypropylene) may be used. The plating underlayer 6 is desirably formed thin in order to suppress the influence on transmission characteristics, and the thickness of the plating underlayer 6 is preferably thinner than the thickness of the insulator 3 . More specifically, the thickness of the plating base layer 6 is preferably 0.5 times or less the thickness of the insulator 3, for example, 0.10 mm or more and 0.20 mm or less. When the thickness of the plating underlayer 6 is 0.10 mm or more, the mechanical strength of the plating underlayer 6 increases, so that breakage of the plating underlayer 6 due to bending can be easily suppressed. Further, if the thickness of the plating underlayer 6 is 0.20 mm or less, the stress applied to the plating layer 41 when the signal transmission cable 1 is bent (the plating underlayer 6 follows the bending of the signal transmission cable 1) Since the stress applied to the plated layer 41 is reduced by bending the plated layer 41, cracks in the plated layer 41 can be easily suppressed.

If there is a gap between the plating base layer 6 and the insulator 3, the transmission characteristics are adversely affected. should be provided. It should be noted that it is possible to observe that the plating base layer 6 is in contact with the outer surface of the insulator 3 with no gap, for example, using an optical microscope or an electron microscope.

In addition, when the signal transmission cable 1 is bent, the plating base layer 6 can move in the longitudinal direction of the cable relative to the bending of the insulator 3 (it can slide in the longitudinal direction of the cable with respect to the insulator 3). It is more desirable to have As a result, when the signal transmission cable 1 is bent, the plated base layer 6 bends while moving relative to the bending of the insulator 3 in the longitudinal direction of the cable, thereby suppressing the occurrence of cracks in the plating layer 41. become. The “crack” referred to here is a crack in the plating layer 41 that occurs in the range from the outer surface of the plating layer 41 to the inner surface of the plating layer 41 (the surface in contact with the insulator 3).

If a crack occurs in the plating layer 41, a phenomenon called co-cracking may occur. is formed, even if the plating layer 41 is cracked, the insulator 3 is not likely to be cracked together, and problems such as poor insulation can be suppressed.

Moreover, the plating base layer 6 is preferably provided in a state in which it is not bonded to the insulator 3 and can be separated from the insulator 3 . This makes it possible to easily peel off the plating layer 41 from the insulator 3 and expose the insulator 3 when processing the terminal of the signal transmission cable 1, thereby improving the workability of terminal processing.

The outer surface of the plating base layer 6 is subjected to a predetermined treatment to form the plating layer 41 . Details of this process will be described later.

(Shield layer 4)
The shield layer 4 has a plating layer (inner shield layer) 41 formed to cover the plating base layer 6 and an outer shield layer 42 provided to cover the plating layer 41 . Note that the outer shield layer 42 may not be provided.

The outer shield layer 42 is made of metal wire, and is made by braiding or laterally winding the metal wire. In the present embodiment, the outer shield layer 42 is composed of a braided shield made of braided metal wires. Metal wires include, for example, annealed copper wires and hard copper wires made of copper or copper alloys. Moreover, it may be a metal wire made of aluminum or an aluminum alloy. The metal wire may be plated on its outer surface. In the present embodiment, the outer shield layer 42 is composed of a single layer, but the outer shield layer 42 may be composed of multiple layers. Moreover, the metal wire forming the outer shield layer 42 may have lubricating properties on its surface. For example, lubricity may be imparted by applying a lubricant such as talc powder to the surface of the metal wire.

By providing the outer shield layer 42, even if the plating layer 41 is damaged by some unexpected damage, the shield layer 4 can be prevented from being electrically insulated. Further, by providing the outer shield layer 42, even if the plated layer 41 is thin, the thickness of the outer shield layer 42 can further reduce the loss of low-frequency signals.

The plating layer 41 constitutes an external conductor together with the outer shield layer 42 and is formed so as to be in direct contact with the outer peripheral surface of the plating base layer 6 . As described above, the outer shield layer 42 is formed by braiding or laterally winding metal wires, but with only the outer shield layer 42, internal signals are radiated to the outside through the gaps between the metal wires. There is a risk that the amount of attenuation will increase. By providing the plated layer 41, the gaps between the metal wires of the outer shield layer 42 are filled, and the attenuation is further reduced. The plated layer 41 and the outer shield layer 42 are in contact and electrically connected.

As the plating layer 41, it is preferable to use a metal having a conductivity of 99% or more (99% IACS or more). For example, a metal such as copper or silver can be used.

The thickness of the plating layer 41 is preferably 2 μm or more and 5 μm or less. When the thickness of the plating layer 41 is 2 μm or more, cracks are less likely to occur in the plating layer 41 even when the outer shield layer 42 and the plating layer 41 come into contact with each other when bending is applied. Further, when the thickness of the plating layer 41 is 5 μm or less, it is possible to prevent the signal transmission cable 1 from becoming difficult to bend due to the hardening of the plating layer 41 .

As shown in FIG. 1B, in the signal transmission cable 1 according to this embodiment, the surface roughness of the outer peripheral surface of the plating layer 41 is smaller than the surface roughness of the inner peripheral surface of the plating layer 41 . The outer peripheral surface of the plating layer 41 is a surface positioned radially outward of the plating layer 41 and is a surface that contacts the outer shield layer 42 . In addition, the inner peripheral surface of the plating layer 41 is a surface positioned radially inward of the plating layer 41 and is a surface in contact with the plating base layer 6 . As shown in FIG. 1B, the plating layer 41 is in contact with the underlying plating layer 6 without any gaps, so the surface roughness of the inner peripheral surface of the plating layer 41 is the surface roughness of the outer peripheral surface of the underlying plating layer 6. I agree with roughness. In addition, FIG.1(b) is the photograph which expanded the cross section of the cable 1 for signal transmission which was produced on trial.

By increasing the surface roughness of the inner peripheral surface of the plating layer 41 , the plating layer 41 is less likely to separate from the plating base layer 6 due to the anchor effect. In the present embodiment, by intentionally roughening the plating underlayer 6, the surface roughness of the inner peripheral surface of the plating layer 41 (that is, the surface roughness of the outer peripheral surface of the plating underlayer 6) is increased. are doing. In order to suppress peeling of the plating layer 41 from the plating base layer 6, the arithmetic mean roughness Ra of the inner surface of the plating layer 41 is preferably 2 μm or more.

In addition, by reducing the surface roughness of the outer peripheral surface of the plating layer 41, when the outer shield layer 42 rubs against the plating layer 41, such as when the signal transmission cable 1 is bent, Wear of the shield layer 42 is suppressed, and damage (cracking) due to wear of the plating layer 41 can be suppressed. The arithmetic mean roughness Ra of the outer peripheral surface of the plating layer 41 is preferably smaller than the arithmetic mean roughness Ra of the inner surface of the plating layer 41, and is preferably less than 2 μm.

By making the surface roughness of the outer peripheral surface of the plating layer 41 smaller than the surface roughness of the inner peripheral surface of the plating layer 41 in this way, the plating layer 41 is not cracked due to wear with the outer shield layer 42 . Even if the plating layer 41 cracks, the plating layer 41 is less likely to peel off from the plating base layer 6, and the transmission characteristics are less likely to deteriorate when the signal transmission cable 1 is bent.

Furthermore, in the present embodiment, the plating layer 41 is formed on the plating base layer 6 made of resin. 6 can slide against the insulator 3 while maintaining a state in which it is in contact with the outer surface of the insulator 3 without gaps, and the distance between the conductor 2 and the plating layer 41 (the distance between the inner conductor and the outer conductor) is kept substantially constant. becomes possible. For example, instead of the plating layer 41 and the plating base layer 6, when a metal tape having a metal layer formed on one side of a resin layer is vertically wrapped, the metal tape may wrinkle or fold due to bending, and the metal tape may become an insulator. A characteristic impedance may change locally due to, for example, a gap between metal tapes, and the return loss may increase due to the mismatch of the characteristic impedance. On the other hand, in the signal transmission cable 1 according to the present embodiment, the plating base layer 6 is flexibly deformed in response to bending, so that the distance between the conductor 2 and the plating layer 41 is kept substantially constant and the signal It is possible to keep the characteristic impedance substantially constant in the cable longitudinal direction of the transmission cable 1, and it is possible to suppress return loss and obtain good attenuation characteristics.

(Method for Forming Plating Layer 41)
2A and 2B are diagrams for explaining the formation of the plating layer 41. FIG. When forming the plating layer 41, first, the first cable substrate 1a is delivered from the delivery drum 10a, and subjected to surface modification treatment. The first cable substrate 1a is formed by sequentially forming an insulator 3 and a plating base layer 6 around a conductor 2. As shown in FIG.

In the surface modification treatment, powder is sprayed on the outer peripheral surface of the plating underlayer 6 by the blasting device 11, and blasting is performed to roughen the outer peripheral surface of the plating underlayer 6 to a predetermined surface roughness. A corona discharge treatment is performed by a corona discharge device 12 to modify (hydrophilize) the surface of the plating underlayer 6 .

As shown in FIGS. 3(a) and 3(b), the blasting apparatus 11 has a plurality (here, four) of nozzles 11a to 11d. By spraying the powder from different directions in the circumferential direction of one cable base 1a, the outer peripheral surface of the plating base layer 6 is configured to have a uniform surface roughness. Here, the four nozzles 11a to 11d are configured to blow the powder to the first cable base 1a from directions different by 90° in the circumferential direction. The number and arrangement of the plurality of nozzles 11a to 11d are not limited as long as the surface roughness is sufficient and blasting can be performed so as not to create a gap between the insulator 3 and the plating underlayer 6. For example, when N nozzles are arranged in the circumferential direction of the first cable substrate 1a, each of the N nozzles is arranged so as to be shifted by an equal angle (360°/N pieces) along the circumferential direction. Let Further, the amount of powder blown out from each of the plurality of nozzles and the air pressure at the time of blowing out may be changed according to the shape of the first cable base 1a. For example, when the shape of the first cable base 1a is circular, the amount of powder and the air pressure sprayed from each of the plurality of nozzles should be the same. As a result, the surface of the plating underlayer 6 has a predetermined surface roughness Ra (for example, a surface roughness Ra of 2) without creating a gap between the insulator 3 and the plating underlayer 6 in the first cable substrate 1a. .0 μm or more). Since the surface of the plating underlayer 6 has a predetermined surface roughness Ra, the inner peripheral surface of the plating layer 41 formed through the pretreatment described later has a surface roughness equal to the surface roughness of the surface of the plating underlayer 6. can be made

Here, dry ice was used as the powder used in the blasting apparatus 11 . However, the powder is not limited to this, and powders composed of metal particles, carbon particles, oxide particles, carbide particles, nitride particles, and the like can also be used.

Returning to FIG. 2, after performing the surface modification treatment, the electroless plating pretreatment is performed. The pretreatment for electroless plating is a pretreatment for forming a film by electroless plating. -Sn catalyst treatment, Pd activation treatment for removing Sn from the adsorbed Pd--Sn colloid, and Pd ion solution immersion treatment for increasing the amount of Pd adsorption are performed in sequence. In the present embodiment, Pd is adsorbed on the outer peripheral surface of the plating underlayer 6 in the electroless plating pretreatment, but the metal to be adsorbed is not limited to Pd, and Pt or Au, for example, can also be used. .

After that, electroless plating is performed by the electroless plating device 14 . In electroless plating, a copper film is formed using Pd adsorbed by pretreatment as a seed. Electroplating is then performed by the electroplating device 15 . In electrolytic plating, a copper film formed by electroless plating is thickened. Thereby, the plating layer 41 is formed. The second cable base 1b with the plating layer 41 formed thereon is wound on the winding drum 10b. After that, the outer shield layer 42 and the sheath 5 are sequentially provided around the plated layer 41 to manufacture the signal transmission cable 1 .

FIG. 4 shows the measurement results of the surface roughness of the outer peripheral surface of the plating base layer 6 after blasting. The surface roughness is measured using a laser microscope (VK8510, manufactured by Keyence Corporation), the measurement area is 200 μm × 100 μm, and the arithmetic average roughness Ra is measured at five locations at intervals of 10 mm in the longitudinal direction of the cable. The average value of the measured values at each point was calculated. In FIG. 4, the average value is indicated by ●, and the dispersion of the five measured values is indicated by an I-shaped bar. As shown in FIG. 4, the arithmetic average roughness Ra of the outer peripheral surface of the plating underlayer 6 is 2 μm or more at any position in the circumferential direction, and the average value is 3 μm or more. . Since the plating layer 41 is formed on the outer peripheral surface of the plating underlayer 6 , the surface roughness of the outer peripheral surface of the plating underlayer 6 is equal to the surface roughness of the inner peripheral surface of the plating layer 41 .

Depending on the conditions of the blasting process, the blasting process may create a gap between the insulator 3 and the plating base layer 6 . Therefore, it is preferable to perform the blasting under conditions that do not create a gap between the insulator 3 and the plating base layer 6 . As a result of studies by the present inventors, when the line speed (conveyance speed) of the first cable substrate 1a is set to 2 m/min and the air pressure in the blasting process is set to 0.5 MPa, the insulator 3 and the plating base layer 6 When the air pressure was set to 0.6 MPa, a gap was formed between the insulator 3 and the plating base layer 6 . Therefore, in this case, it is desirable that the air pressure for blasting is less than 0.6 MPa, more preferably 0.5 MPa or less.

(Transmission characteristics of signal transmission cable 1)
A sample of the signal transmission cable 1 shown in FIG. 1 without the outer shield layer 42 and the sheath 5 was manufactured as a trial, and the transmission characteristics were measured. First, transmission loss (insertion loss) S21 was measured. The measurement of S21 was performed for the case where the signal transmission cable 1 was straight without bending (unbent) and the case where the signal transmission cable 1 was bent with a bending radius R of 1 mm. The measurement results are shown in FIGS. 5(a) and 5(b), respectively.

As shown in FIGS. 5(a) and 5(b), it can be seen that S21 when the prototype sample is bent with a bending radius of R=1 mm is substantially the same as that in the straight state. More specifically, the change in S21 in a state bent with a bending radius R of 1 mm with respect to S21 in a straight state was as small as 0.4 dB or less at a frequency of 28 GHz. Although not shown, S21 was measured by changing the bending radius R from 40 mm to 1 mm. was very small, and was almost the same as the change in S21 when bent with a bending radius R of 1 mm.

Next, changes in characteristic impedance were measured in the straight state and in each case where the bending radius R was changed from 40 mm to 1 mm. The results are summarized in FIG. 6(a). As shown in FIG. 6A, when the bending radius R is 2.5 mm or less, the characteristic impedance slightly changes at the bent portion.

The S21 at 28 GHz (S21@28 GHz) and the characteristic impedance of the bent portion are collectively shown in FIG. 6(b). As shown in FIG. 6(b), when the bending radius R is reduced to 2.5 mm or less, S21 and characteristic impedance slightly change, but the change is slight. Moreover, when the bending radius R is 5 mm or more, it can be seen that S21 and the characteristic impedance are almost the same as in the straight state. From the above, it was confirmed that the signal transmission cable 1 whose transmission characteristics are less likely to deteriorate when bent has been realized.

(Actions and effects of the embodiment)
As described above, the signal transmission cable 1 according to the present embodiment includes the plating base layer 6 provided between the insulator 3 and the shield layer 4 so as to cover the periphery of the insulator 3, The shield layer 4 has a plating layer 41 formed so as to be in contact with and cover the outer peripheral surface of the plating underlayer 6, and the surface roughness of the outer peripheral surface of the plating layer 41 is equal to that of the plating. It is smaller than the surface roughness of the inner peripheral surface of layer 41 .

By configuring in this way, wrinkles in the shield layer during bending are suppressed as in the case where a tape member is used for the shield layer as in the conventional technology, and transmission characteristics are reduced when bent. become difficult. Furthermore, even when the outer shield layer 42 is provided, cracking of the plating layer 41 due to abrasion with the outer shield layer 42 can be suppressed, and even if the plating layer 41 cracks, Also, the plating layer 41 is less likely to peel off from the plating base layer 6 . As a result, it is possible to realize the signal transmission cable 1 whose transmission characteristics are less likely to deteriorate when bent.

(Summary of embodiment)
Next, technical ideas understood from the embodiments described above will be described with reference to the reference numerals and the like in the embodiments. However, each reference numeral and the like in the following description do not limit the constituent elements in the claims to the members and the like specifically shown in the embodiment.

[1] A conductor (2), an insulator (3) that surrounds the conductor (2), a shield layer (4) that surrounds the insulator (3), and a periphery of the shield layer (4) A signal transmission cable (1) comprising a sheath (5) covering a The shield layer (4) is in contact with the outer peripheral surface of the plating underlayer (6) and covers the plating underlayer (6). A signal transmission cable ( 1 ).

[2] The signal transmission cable (1) according to [1], wherein the plating base layer (6) is thinner than the insulator (3).

[3] The signal transmission cable (1) according to [1] or [2], wherein the inner peripheral surface of the plating layer (41) has an arithmetic mean roughness Ra of 2 μm or more.

[4] The signal transmission cable (1) according to any one of [1] to [3], wherein the insulator (3) is made of fluororesin, and the plating base layer (6) is made of polyethylene or polypropylene. ).

Although the embodiments of the present invention have been described above, the embodiments described above do not limit the invention according to the scope of claims. Also, it should be noted that not all combinations of features described in the embodiments are essential to the means for solving the problems of the invention. Moreover, the present invention can be modified appropriately without departing from the gist thereof.

DESCRIPTION OF SYMBOLS 1... Signal transmission cable 2... Conductor 3... Insulator 4... Shield layer 41... Plating layer 42... Outer shield layer 5... Sheath 6... Plating foundation layer

Claims (4)

a conductor;
an insulator surrounding the conductor;
a shield layer surrounding the insulator;
A signal transmission cable comprising a sheath that surrounds the shield layer,
A plating base layer provided between the insulator and the shield layer so as to cover the periphery of the insulator,
The shield layer has a plating layer formed so as to be in contact with the outer peripheral surface of the plating underlayer and to cover the plating underlayer,
The surface roughness of the outer peripheral surface of the plating layer is smaller than the surface roughness of the inner peripheral surface of the plating layer,
Cable for signal transmission. The thickness of the plating underlayer is thinner than the thickness of the insulator,
The signal transmission cable according to claim 1. The arithmetic mean roughness Ra of the inner peripheral surface of the plating layer is 2 μm or more,
The signal transmission cable according to claim 1 or 2. the insulator is made of fluororesin,
The plating underlayer is made of polyethylene or polypropylene,
The signal transmission cable according to any one of claims 1 to 3.

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